基于Mie谐振耦合的亚波长金属孔透射光增强

Enhanced optical transmission through a metallic subwavelength aperture, breaking through the limitation of the classical aperture theory, has a great prospect in the flat panel display, spectral imaging, and solar cells. However, this enhanced transmission, based on surface plasmon polariton (SPP), has many shortcomings such as narrow bandwidth and high loss. Therefore, the realization of the enhanced transmission base on non-SPP is urgent. In this project, the very low loss silicon material in optical band and the principle of the electromagnetic resonance coupling was used to realize the enhanced transmission. By placing silicon nanoparticles with a certain shape and size in the metallic subwavelength apertures periodically arranged in the two-dimensional metal film, Mie resonance effect of the silicon nanoparticles was produced so that the incident light was localized in the subwavelength scale of the nanoparticles, which form the equivalent electromagnetic dipoles with a high energy density. Then, the energy of the equivalent electromagnetic dipoles was radiated through the aperture, thus the transmitted light was enhanced and the frequency of the transmission peak can be adjusted by silicon nanoparticle size. This project proposed enhanced transmission, based on Mie resonance coupling of the silicon nanoparticles, has many advantages such as high transmission efficiency, low loss, and strong compatibility with the current semiconductor processes, and has a broader significance for the enhanced transmission of light through the metal subwavelength aperture.

亚波长金属孔的光学异常透射现象突破了经典孔径理论的限制，在平板显示、光谱成像、太阳能电池等方面具有巨大的应用前景，但这种由金属表面等离子体引起的透射增强存在带宽窄、损耗高等缺点，因此迫切需要研究基于非表面等离子体实现的亚波长金属孔透射光增强。本项目拟采用光频段损耗极低的硅材料和电磁波的谐振耦合原理实现亚波长金属孔的透射光增强，通过在周期性排列的二维亚波长金属孔内部放置具有一定形状和大小的硅纳米颗粒，由硅纳米颗粒产生的Mie谐振效应把入射光局域在颗粒的亚波长尺度范围内，形成能量密度极高的等效电磁偶极子，然后通过小孔辐射出去，藉此实现硅纳米颗粒尺寸大小决定的频率可调透射光增强。这种基于硅纳米颗粒Mie谐振耦合实现的透射增强，具有传输效率高、损耗低、与现有半导体工艺兼容性强等优点，对于亚波长金属孔的透射增强具有更加广泛的意义。

本项目采用放置在金属孔两边的硅纳米颗粒的Mie谐振耦合取代表面等离激元共振，实现亚波长金属孔的宽带高透射传输。项目研究结果表明，采用Mie谐振耦合的亚波长金属孔(r/λ=0.1)光传输，透射系数超过90%的带宽达到65 nm，与表面等离激元共振诱导的透射增强相比，峰值增高了1.5倍，3dB带宽拓宽了17倍。根据耦合模理论，建立了Mie谐振耦合亚波长金属孔透射的等效电路模型，并在临界耦合状态下反演出电路模型中的元件参数值。进一步研究发现，仅通过改变等效电路模型中的耦合系数，就可全面揭示Mie谐振耦合亚波长金属孔透射的传输规律，并得到与全波电磁仿真完全一致的结果，从而找到光与放置硅纳米颗粒的亚波长金属孔相互作用的数学表达，也给予人们在光学领域按照电路设计方法构建相应功能模块的启示。